If he's looking for idea introduce him to this site or show him the following thread. I know I've been inspired many times from that thread. Best advice you could give him is to look around and see what he takes interest in. https://www.cointalk.com/threads/lets-see-your-newest-acquisitions.158772/page-834#post-2271321
I would walk him through a Red Book and see if there are any U.S coin designs that he really likes. World coins are a good choice too, but with all the choices, for a first coin, I think I'd stay with a U.S. coin. If he "takes" to the hobby, he can always venture out into world or ancient coins. Once you've settled on a design then you can begin having a value discussion. Do you want rarity or a common coin in higher grade?
To this type of question, I almost invariably come up with the same answer . . . Buy obsolete 90% silver (about 200 Mercury Dimes would be a good example in this case), go through it and start building a set with what is there. Then sell off what is left over after contributing to the set, and start again. Eventually, the set might be half complete at little or no cost over silver. Then it will be time to spend larger sums on those which are harder to locate. This will probably maximize enjoyment and minimize the total cost thereof.
I will gladly sell him this coin for $300.00 and in my opinion it's the best one he can buy! (in all seriousness, the answer is entirely subjective - and there are many people that would be happy to fleece him of his $300 if he allows them)